There is known a spark plug provided with an identifier (mark) defined in advance, in order to prevent erroneous mounting of the spark plug to an engine or allow tracking of history information about the spark plug. In technology disclosed in Japanese Patent Application Laid-Open (kokai) No. 2012-128948, a spark plug has a projection projecting rearward from the outer edge of the bottom surface of a metal terminal that faces the rear side, and a mark is provided to the bottom surface of the metal terminal. Owing to the projection, an external force which can lead to peeling or damage of the mark is less likely to be exerted on the bottom surface, so that peeling or damage of the mark is suppressed. Thus, occurrence of reading error of the mark can be suppressed.
For this type of spark plug, technology for further suppressing peeling or damage of the mark is being required.
The present invention has been made to address such requirements. An advantage of the present invention is a spark plug that enables the effect of suppressing peeling or damage of the mark.